The present invention relates to a self-contained change speed apparatus for use on a bicycle which has a change speed device that can be conveniently controlled by the user to change the revolving speed of the wheel hub.
Self-contained change speed apparatus for use on a bicycle are known, for example, from U.S. Pat. Nos. 5,322,487; 5,273,500. Conventional self-contained change speed apparatus for use on a bicycle commonly comprise a planetary gear train for producing different speed ratio, and a clutch for controlling the power transmission path. The power input links for the planetary gear train includes an annular gear and a carrier. According to the kinematic characteristic of a planetary train, the turning direction of the sun gear will be changed when a driving power is transmitted through a different power input link. Therefore, one sun gear must be matched with two reversed one-way pawls, i.e., one one-way pawl for forward rotation control and the other for backward rotation control. Further, when the rotary power from the pedal mechanism of the bicycle is continuously transmitted to the planetary gear train, much power must be employed to the control device for changing the speed. According to the power curve of the pedal mechanism, the input power produced from the pedal mechanism when the crank of the pedal mechanism is at the top or bottom dead point is smaller than the input power when the crank is at the other positions. Therefore less power is required for changing the speed when the crank of the pedal mechanism is at the top or bottom dead point. The aforesaid U.S. Pat. No. 5,322,487 utilizes this characteristic, and employs a spring set between the power input device and the control member for storing energy. The spring stores a shift of the control member as energy. When the crank of the pedal mechanism of the bicycle reaches the top or bottom dead point, the spring releases its stored energy to achieve a speed change. However, this design tends to cause a speed change behindhand.